Programmable electrical fuse

ABSTRACT

The present invention relates to e-fuse devices, and more particularly to a device and method of forming an e-fuse device, the method comprising providing a first conductive layer connected to a second conductive layer, the first and second conductive layers separated by a barrier layer having a first diffusivity different than a second diffusivity of the first conductive layer. A void is created in the first conductive layer by driving an electrical current through the e-fuse device.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.12/135,242, filed Jun. 9, 2008 the entire content and disclosure ofwhich is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a programmable electronic fuse (e-fuse)device, and more particularly to a device and method of programming ane-fuse device by driving an electrical current through a firstconductive layer, a barrier layer and a second conductive layer tocreate a void in the first conductive layer.

BACKGROUND OF THE INVENTION

Computers and related electronic equipment typically have a number ofdifferent types of data storage or memory devices. For example, a readonly memory (ROM) is a semiconductor memory device in which data ispermanently stored. The data stored on ROM cannot be overwritten orotherwise altered by the user. A ROM is also non-volatile, which meansthat the data is not destroyed when power is lost. A ROM is programmedduring its manufacture by making permanent electrical connections inselected memory cells. ROMs are useful wherever unalterable data orinstructions are required. A disadvantage of ROMs is that theirprogramming is determined during the design stage and can only be variedby redesigning the chip.

An alternative to a ROM is a programmable read only memory (PROM) whichis programmable once after its manufacture. In one type of PROM, eachmemory cell is provided with an electrical connection in the form of afusible link. The PROM is programmed by blowing the fusible link inselected cells. To blow the fuse, current is driven through the link.The current heats the link to its melting point and the link is broken.Usually the link breaks in thinner regions where the current density ishighest.

Various means have been used in the past to blow electrically blowablefuses. One recently used technique for opening the connection at thefuse employs the electro-migration effect, which has long beenidentified as a major metal failure mechanism. Electro-migration is theprocess whereby the ions of a metal conductor move in response to thepassage of a high-density current flow though the conductor. Such motioncan lead to the formation of voids in the conductor, which can grow to asize where the conductor is unable to pass current. One can takeadvantage of the electro-migration effect to selectively open up metalconnections (e.g., fuses) at desired locations within an integratedcircuit.

However, prior art e-fuse devices using electrically parallel layers ofsilicon and poly-silicon, as well as W-contact structures, are not asdesirable because they require high temperature and high power, whichcauses damage to neighboring elements.

Therefore, there is a need in the art for an e-fuse device featuring alow voltage, low temperature programming process that is lessdestructive to neighboring devices.

SUMMARY OF THE INVENTION

The present invention relates to e-fuse devices, and more particularlyto a structure and method of forming an e-fuse device, the methodcomprising providing a first conductive layer connected to a secondconductive layer, the first and second conductive layers separated by abarrier layer having a first diffusivity different than a seconddiffusivity of the first conductive layer. A void is created in thefirst conductive layer by driving an electrical current through thee-fuse device.

Specifically, and in broad terms, an e-fuse device is disclosed, thedevice comprising:

a first conductive layer connected to a second conductive layer; and

a barrier layer between the first and second conductive layers, thebarrier layer having a first diffusivity and the first conductive layerhaving a second diffusivity different than the first diffusivity forcreating a void in the first conductive layer in response to anelectrical current driven through the e-fuse device.

In a related aspect, the first diffusivity of the barrier layer is lowerthan the second diffusivity of the first conductive layer.

In a related aspect, the e-fuse device further comprises an insulatinglayer between the first conductive layer and the second conductivelayer.

In a related aspect, the first conductive layer, the barrier layer andthe second conductive layer are electrically connected in series by avia formed through the insulating layer.

In a related aspect, the barrier layer is located along a bottom surfaceand a sidewall surface of the via in a U-shaped configuration.

In a related aspect, the via comprises a spacer adjacent the barrierlayer.

In a related aspect, the first conductive layer extends into the via toa point in the insulating layer.

In a related aspect, the first and second conductive layers comprise oneof copper, aluminum and aluminum-copper alloy.

In a related aspect, the barrier layer comprises one of tantalum,tantalum nitride, titanium, titanium nitride and tungsten.

In a related aspect, a diffusivity of the second conductive layer islower than the second diffusivity of the first conductive layer.

Another aspect of the present invention relates to a method of formingan e-fuse, the method comprising:

providing a first conductive layer connected to a second conductivelayer, the first and second conductive layers separated by a barrierlayer having a first diffusivity different than a second diffusivity ofthe first conductive layer; and

-   -   creating a void in the first conductive layer by driving an        electrical current through the e-fuse device.

Another aspect of the present invention relates to a method ofprogramming an e-fuse device, the method comprising: driving anelectrical current through a first conductive layer, a barrier layer,and a second conductive layer to create a void in the first conductivelayer, wherein the barrier layer has a first diffusivity and the firstconductive layer has a second diffusivity different than the firstdiffusivity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a layout top view illustrating a programmable e-fuse deviceaccording to an embodiment of the invention.

FIG. 2 is a cross sectional view illustrating the programmable e-fusedevice of FIG. 1.

FIG. 3 is a partial cross-sectional view showing formation of a voidaccording to the programming method of the present invention.

FIG. 4 a is a cross sectional view illustrating a portion of theprogrammable e-fuse device of FIG. 2 before programming.

FIG. 4 b is a cross sectional view illustrating the portion of theprogrammable e-fuse device in FIG. 4 a after programming.

FIG. 5 a is a cross sectional view illustrating another embodiment of aprogrammable e-fuse before programming.

FIG. 5 b is a cross sectional view illustrating the programmable e-fuseof FIG. 5 a after programming.

DETAILED DESCRIPTION OF THE INVENTION

The present invention, which provides an e-fuse device and a method ofprogramming the e-fuse device, will now be described in greater detailby referring to the drawings that accompany the present application. Itis noted that the drawings of the present application are provided forillustrative purposes and are thus not drawn to scale. The figures shownand described illustrate a relatively small portion of a largersemiconductor, which includes associated circuitry not shown. Theinvention may be understood in the context of a conductive path betweenelements in a more complex circuit that may be comprised of numerousadditional components constructed according to the invention. Moreover,like and corresponding elements shown in the drawings are referred to bylike reference numerals.

Referring first to FIGS. 1-2, an e-fuse device 100 according to thepresent invention will now be described. As shown, the e-fuse device 100comprises a first conductive layer 20 electrically connected to a secondconductive layer 24. The first and second conductive layers 20, 24 maybe formed using deposition processes well known in the art including,but not limited to, chemical vapor deposition (CVD), low pressure CVD(LPCVD), and high-density chemical vapor deposition (HDCVD), physicalvapor deposition (PVD), electroplating or a combination thereof. It isassumed for the purposes of describing the examples of the inventionherein that the first and second conductive layers 20, 24 may beconnected to reference voltage potentials by associated circuitry (notshown) for driving an electrical current through the e-fuse device 100.

The first and second conductive layers 20, 24 are separated by aninsulating layer 28 typically composed of a dielectric material such as,but not limited to, crystalline oxide, non-crystalline oxide, porousdielectrics, nitride or any other suitable material formed and patternedto provide a via 16 and a set of vias 18 extending to the firstconductive layer 20. The set of vias 18 connects a first section 20 a ofthe first conductive layer 20 to the second conductive layer 24, whilethe via 16 connects a second section 20 b of the first conductive layer20 to the second conductive layer 24.

Current flows from the first section 20 a of the first conductive layer20 into the second conductive layer 24 through the set of vias 18. Eachvia in the set of vias 18 provides a separate parallel current path froma voltage reference potential into the second conductive layer 24. Allof these parallel current paths converge at the via 16 seeking a returnpath through the first conductive layer 20 and a barrier layer 40 (to bedescribed in greater detail herein below) positioned between the firstand second conductive layers 20, 24. The first conductive layer 20, thebarrier layer 40 and the second conductive layer 24 are electricallyconnected in series by the via 16, which provides the only current pathout of the second conductive layer 24. The via 16 and the secondconductive layer 24 may be composed of a metal material susceptible toelectro-migration, e.g., copper, aluminum or aluminum copper alloy. Itwill be understood by those with skill in the art that the via 16 andthe second conductive layer 24 may comprise the same or differentmaterials and may be formed in a single processing step.

Turning now to FIG. 3, a partial cross-sectional view showing formationof a void 45 according to the programming method of the presentinvention will be described in further detail. As shown, the barrierlayer 40 is located between the first and second conductive layers 20,24. The barrier layer 40 has a first diffusivity, while the firstconductive layer 20 has a second diffusivity different than the firstdiffusivity for creating the void 45 in the first conductive layer 20 inresponse to an electrical current through the e-fuse device 100. Whensufficient programming current is provided, the atoms in the firstconductive layer 20 near the barrier layer 40 migrate away from thebarrier layer 40, creating an electrical open. Based on this diffusiondifferential between barrier layer 40 and the first conductive layer 20,the void 45 is created in the first conductive layer 20. It will beunderstood by those with skill in the art that programming conditions(e.g., voltage, current, temperature, etc.) can be modified as necessaryto achieve the desired void 45 size.

The first and second conductive layers 20, 24 may be composed of a metalmaterial susceptible to electro-migration, e.g., copper, aluminum oraluminum copper alloy. It will be understood by those with skill in theart that the first and second conductive layers 20, 24 may comprise thesame or different materials. In an exemplary embodiment of theinvention, the first and second conductive layers 20, 24 comprisedifferent materials, each having a different diffusivity. Thediffusivity of the first conductive layer 20 is higher than thediffusivity of the second conductive layer 24. As such, the material ofthe first conductive layer 20 is more susceptible to electro-migrationthan the material of the second conductive layer 20, and the void 45 isformed in the first conductive layer 20 during programming.

The barrier layer 40 is less sensitive to electro-migration and acts asa diffusion block due to its relatively high atomic diffusion resistanceas compared to the first and second conductive layers 20, 24. Thebarrier layer 40 may be comprised of a material such as, but not limitedto, tantalum, tantalum nitride, titanium, titanium nitride, tungsten,aluminum and aluminum-copper alloy, or a combination thereof.Preferably, the barrier layer 40 is a tantalum-nitride layer formed bychemisorbing monolayers of a tantalum containing compound and a nitrogencontaining compound.

Referring now to FIGS. 4 a-4 b, a section 35 of the e-fuse device 100(represented by dashed line 35 in FIG. 2), including via 16 and thesecond portion 20 b of the first conductive layer 20, will be describedin greater detail. As shown, the barrier layer 40 is located between thefirst and second conductive layers 20, 24 and is formed along the bottomsurface 44 and the sidewall surface 48 of via 16 in a U-shapedconfiguration. The barrier layer 40 has a first diffusivity, while thefirst conductive layer 20 has a second diffusivity different than thefirst diffusivity for creating a void 45 (shown in FIG. 4 b) in thefirst conductive layer 20 in response to an electrical current throughthe e-fuse device 100. As discussed above, the barrier layer 40 is lesssensitive to electro-migration and acts as a diffusion block due to itsrelatively high atomic diffusion resistance as compared to the first andsecond conductive layers 20, 24. Based on this diffusion differentialbetween barrier layer 40 and the first conductive layer 20, the void 45is created in the first conductive layer 20 and the resistance of thee-fuse device 100 is significantly increased.

The e-fuse device 100 is particularly useful for metal gate applicationshaving no polysilicon. For example, by providing a tantalum or tantalumnitride barrier layer 40 between copper conductive layers 20 and 24,less current is required to form the void 45 than is required in ane-fuse device having a polysilicon conductive layer. Furthermore, thee-fuse device 100 of the present invention and the choice of materialsallows the e-fuse device 100 to be easily incorporated into existingBEOL processes. Therefore, the present invention provides alow-temperature, non-destructive programming process that increases theresistance of the e-fuse device 100, while reducing damage onneighboring elements.

Referring now to FIGS. 5 a-5 b, another embodiment of the invention willbe described in more detail. A complete description of features incommon with the embodiment shown in FIGS. 1-3 will be dispensed with forthe sake of brevity. As shown in FIGS. 5 a-5 b, the via 116 may comprisea spacer 166 adjacent the barrier layer 140. The spacer 166 may be adielectric spacer comprised of a material such as, but not limited to,crystalline oxide, non-crystalline oxide, or nitride. The spacer 166 isformed along the sidewall surfaces 148 of the via 116 usingconventionally known techniques to define the diameter of the via 116.

Furthermore, the first conductive layer 120 of the e-fuse device 200extends into the via 116 to a point 162 in the insulating layer 128. Thebarrier layer 140 has a first diffusivity, while the first conductivelayer 120 has a second diffusivity different than the first diffusivityfor creating the void 145 in the first conductive layer 120 in the via116. Based on this diffusion differential between barrier layer 140 andthe first conductive layer 120, the void 145 is created in the via 116.Forming the void 145 within the via 116 allows for controlled expansionof the void 145, thus providing greater control over the resistance ofthe e-fuse device 200.

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood byone skilled in the art that the foregoing and other changes in forms anddetails may be made without departing from the spirit and scope of theinvention. It is therefore intended that the present invention is notlimited to the exact forms and details described and illustrated, butfalls within the spirit and scope of the appended claims.

What we claim is:
 1. An electrical-fuse (e-fuse) device comprising: a first conductive layer connected to a second conductive layer; and a barrier layer between the first conductive layer and the second conductive layer, the barrier layer having a first diffusivity and the first conductive layer having a second diffusivity different than the first diffusivity for creating a void in the first conductive layer in response to an electrical current driven through the e-fuse device.
 2. The e-fuse device of the claim 1, wherein the first diffusivity of the barrier layer is lower than the second diffusivity of the first conductive layer.
 3. The e-fuse device of claim 1, further comprising an insulating layer between the first conductive layer and the second conductive layer.
 4. The e-fuse device of claim 1, wherein the first conductive layer, the barrier layer and the second conductive layer are electrically connected in series by a via in the insulating layer.
 5. The e-fuse device of claim 4, wherein the barrier layer is located along a bottom surface and a sidewall surface of the via in a U-shaped configuration.
 6. The e-fuse device of claim 4, wherein the via comprises a spacer adjacent the barrier layer.
 7. The e-fuse device of claim 1, wherein the first and second conductive layers comprise one of copper, aluminum and aluminum-copper alloy, and wherein the barrier layer comprises one of tantalum, tantalum nitride, titanium, titanium nitride and tungsten.
 8. The e-fuse device of claim 1, wherein the first conductive layer extends into the via to a point in the insulating layer.
 9. The e-fuse device of claim 1, wherein a diffusivity of the second conductive layer is lower than the second diffusivity of the first conductive layer.
 10. A method of programming an electrical-fuse (e-fuse) device comprising: driving an electrical current through a first conductive layer, a barrier layer, and a second conductive layer to create a void in the first conductive layer, wherein the barrier layer has a first diffusivity and the first conductive layer has a second diffusivity different than the first diffusivity.
 11. The method of claim 10, further comprising an insulating layer between the first and second conductive layers.
 12. The method of claim 11, wherein the first conductive layer, the barrier layer and the second conductive layer are electrically connected in series by a via formed in the insulating later.
 13. The method of claim 12, wherein the barrier layer is formed along a bottom surface and a sidewall surface of the via in a U-shaped configuration.
 14. The method of claim 10, wherein a diffusivity of the second conductive layer is lower than the diffusivity of the first conductive layer. 